Update eslint and eslint-config-cesium

[ggetz]

Description

Following up from https://github.com/CesiumGS/eslint-config-cesium/pull/6, this bumps the version of eslint and corresponding packages. The major change is a migration from .eslintrc.js files to flat config files.

Other notable changes include:

• Added a package.json and corresponding config to .github/actions/check-for-cla. This was mainly to make eslint happy, but is probably better practice anyway to ensure version compatibility with dependencies.
• Removed outdated inline eslint comments where found
• Bumped minimum supported version for compatibility, which matches the current LTS of NodeJS anyway

Issue number and link

N/A

Testing plan

1. Run npm eslint and confirm there are no issues
2. Introduce an eslint error to ensure that errors still surface when running npm eslint.

Author checklist

• [x] I have submitted a Contributor License Agreement
• [x] I have added my name to CONTRIBUTORS.md
• [-] ~I have updated CHANGES.md with a short summary of my change~
• [-] ~I have added or updated unit tests to ensure consistent code coverage~
• [-] ~I have update the inline documentation, and included code examples where relevant~
• [x] I have performed a self-review of my code

[github-actions[bot]]

Thank you for the pull request, @ggetz!

:white_check_mark: We can confirm we have a CLA on file for you.

[jjspace]

@ggetz make-zip is failing for a missing .eslintignore file

[ggetz]

@jjspace This should be ready for another look.

[jjspace]

Apparently prettier didn't like that merge but I touched it up quick.

LGTM, thanks @ggetz!